Predictions of Genes Conferring Resistance to Puccinia hordei in an International Barley Panel Using Gene-for-Gene-Based Postulations and Linked Molecular Markers

Deployment of resistant barley cultivars is the most cost-effective and environmentally responsible strategy to manage barley leaf rust caused by <i>Puccinia hordei</i>. Gene predictions based on screening of germplasm with an array of well-characterised pathotypes and application of molecular markers serve as a pivotal step for identification, characterisation, and deploying resistance in breeding programmes. We evaluated 77 barley genotypes from 17 countries using an array of diverse <i>P. hordei</i> pathotypes and molecular markers to predict resistance gene identities. Evaluation and resistance analysis of the panel determined four known all-stage resistance (ASR) genes-<i>Rph2</i>, <i>Rph3</i>, <i>Rph9.am</i>, and <i>Rph25</i> present individually or in combination, with <i>Rph3</i> being the most common (33% of entries) and <i>Rph2</i> the second most frequent (9%). Three entries, CG55, CG56, and CG57, exhibited low infection to all tested pathotypes and were negative for markers associated with <i>Rph7</i>, <i>Rph15</i>, and <i>Rph28</i>, potentially carrying novel uncharacterised resistance. In addition to ASR, our studies demonstrated that the core panel had a high prevalence of adult plant resistance (APR) to <i>P. hordei</i>, occurring in ~83% of entries. By employing markers linked to APR, we were able to partition known APR with <i>Rph24</i> found in the most lines (60%), followed by <i>Rph23</i> (17%), <i>Rph20</i> (14%), and uncharacterised (9%) either individually or in combination. The resistance sources identified in this study can be effectively utilised and combined by breeding programmes to diversify their resistance gene pool. Our study also revealed the virulence and avirulence profiles of 12 Australian <i>P. hordei</i> pts to catalogued <i>Rph</i> genes, providing pathologists and breeders with insights into combining genes relevant to their breeding regions and pathogen shifts.